The economic wellbeing of pork producers not only depends on the cost of feed and the market price for pork, but also on the ability to attain a high percentage of live births and pigs weaned per litter. However, the producer's success for making a profit is contingent on controlling the cost of personnel to assist in the farrowing operation. Thus, maximum utilization of assisting personnel experienced in farrowing is an important factor. Any significant technological advance to improve this factor is assured of being significant to the producer and of receiving wide acceptance.
Having experienced and skilled personnel available to assist during farrowing and the critical neonatal period is critical for several reasons. Often when giving birth to large litters a sow will tire. This can result in the stillbirth of the last few pigs of the litter who are unable to escape the uterus and reach the air before suffocating. Further, pigs are born virtually without hair and, as such, are very susceptible to temperature changes. Colder temperatures can often cause the death of young pigs.
It should also be appreciated that the litter may be larger than the number of functional nipples available on the sow. Nipples on the upper chest are also typically more productive than those at the hindquarter. Thus, small pigs that can't compete with their litter mates may be pushed to the less productive (or even non-productive) nipples and not receive the nutrients needed to grow properly, or possibly not even survive. Specifically, since pigs are not born with but instead receive their immunity through the milk of the sow, undernourished pigs are very susceptible to diseases and infections. Further, even weakened pigs that are able to survive the cold or disease may, however, be slowed and unable to move quickly enough and actually be accidentally crushed by the sow in the pen.
With proper care, it is known that pig survival can be greatly increased. The assisting personnel can help the sow as she farrows thereby keeping her from tiring and reducing the number of stillborn. The personnel can also clean any obstructions such as mucous from the nostrils of newborn pigs to reduce stress and/or even prevent suffocation. Since sows are receptive to pigs even born of another sow, cross-fostering of pigs can be practiced. By evening the number of pigs per sow and placing pigs of approximately the same size with the same sow, better overall nutrition of all the newborn pigs is assured.
From the above it should be appreciated that the concerns of the producer for personnel efficiency and pig survival are essentially in conflict. Recognizing this, producers for a number of years have sought to synchronize farrowing among sows in a herd as much as possible so as to reduce the man-hours required to provide care and increase newborn pig survival.
In the past, synchronized weanings have been used in an effort to synchronize subsequent farrowings. Specifically, after the sows have all been nursing present litters for about three weeks, weaning takes place. Four to six days after weaning, the sows are again ready for breeding. By breeding all the sows on or about the same day, farrowings can be synchronized to fall within a relatively short period.
While this technique is more efficient from the standpoint of utilizing the assisting personnel than random breeding, due to biological variations in time from weaning to estrus and gestation length, the subsequent farrowings of the sows of the herd can still be expected to take place over a period of as much as seven days duration (note FIG. 1, Bar Chart A). Since farrowings can take place any time day or night, assisting personnel may not always be available from the pool of qualified personnel to help the sows and pigs during this extended period and, of course, the cost for round-the-clock attention, if available, is prohibitive. Thus, more effective methods of synchronizing farrowings are desired to further increase labor efficiency and pig survival.
In order to achieve this improved result, it is necessary to either (1) delay the farrowing of those sows that would normally farrow during the early days of this period or (2) induce farrowing of those sows that would normally farrow during the latter days of the period or (3) both delay and induce farrowings as in numbers 1 and 2 above.
It is well known that progestins may be administered to sows late in the gestation period so as to extend gestation and delay farrowing. It is also well established that prostaglandin (PGF.sub.2.alpha.) may be administered to sows so as to induce parturition or farrowing. There, however, are distinct disadvantages to each of these treatments.
The utilization of progestins to delay farrowing has been shown to be effective but with a resulting increase in stillbirths and incidents of dystocia or abnormal labor. Minar, V. M. and E. Schilling, 1970, "Die Beeinflussung des Gerburtstermins Beim Schwein Durch Gestagene Hormone", Deutsch, Tierarztl, Wschr. 77:428 and Nellor, J. E., R. W. Daniels, J. A. Hoefer, D. E. Wildt and W. R. Dukelow, 1975, "Influence of Induced Delayed Parturition on Fetal Survival in Pigs", Theriogenology 4:23. Because of the increase in stillbirths and the overall reduced survival of the newborn pigs, progestin treatments to delay farrowings are not feasible for utilization in a method to synchronize farrowings where increased pig survival is a desired result.
The utilization of prostaglandin to induce farrowings has also been shown to be effective. The use of prostaglandin to synchronize farrowings in a herd is, however, only of limited effectiveness. Specifically, piglets of induced farrowings born two to three days before the normal term have normal survival and normal birth and weaning weights. Pigs induced to birth more than three days before normal term, however, are underdeveloped at birth and have reduced survival and reduced birth and weaning weights. As such, induced farrowing with prostaglandin can only be effectively utilized to synchronize farrowings without adversely effecting pig survival rates over a three day period. Thus, for a herd of sows bred at synchronized weaning, prostaglandin treatment of only those sows expected to wean on the second through fourth days of the farrowing period is feasible (note FIG. 1, Bar Chart B). A second prostaglandin treatment of those sows expected to wean on days five through seven is, therefore, also necessary if the pig survival rate is to be maintained at a high level. Since a few of the sows also farrow early due to biological variation, personnel must still be available for a large number of hours if the proper care is to be given to the sows and piglets during farrowing and the neonatal period.
A method for both delaying farrowing with progesterone followed by inducing farrowing with prostaglandin to synchronize the farrowings has been proposed by Gooneratne, et al. 1979, in Control of Parturition in the Sow using Progesterone and Prostaglandin, Aust. J. Biol. Sci. 32:587. Although these authors claim the procedure has no significant detrimental effects, the incidence of stillbirths from progesterone-treated sows was threefold greater than in untreated sows. Thus, just as discussed above, the utilization of progesterone to delay farrowing is again shown to produce unacceptable survival rates in the newborn pigs. Apparently others have also found this to be true and as a result this method of synchronizing farrowing is not utilized to any significant extent.
A need is, therefore, clearly identified for a safer and more effective method and composition for delaying farrowing in individual sows and for better synchronizing of farrowings throughout the herd.